Method of production of monocyclohexylamine



United States Patent 3,415,881 METHOD OF PRODUCTION OFMONOCYCLOHEXYLAMINE Andrew P. Dunlop, Riverside, Donald G. Manly,Barrington, and Fred J. Rice, Jr., Carpentersville, Ill., assignors toThe Quaker Oats Company, Chicago, IEL, a corporation of New Jersey NoDrawing. Continuation of application Ser. No. 390,222, Aug. 17, 1964.This application Dec. 18, 1967, Ser. No. 691,649

5 Claims. (Cl. 260563) ABSTRACT OF THE DISCLOSURE Monocyclohexylamine isproduced by reacting cyclohexanone with ammonia and hydrogen in anammoniahydrogen gas mixture and in the presence of a hydrogenationcatalyst and dicyclohexylamine.

This is a continuation of Ser. No. 390,222, filed Aug. 17, 1964, nowabandoned.

This invention relates to a method for the production ofmonocyclohexylamine. More particularly, it relates to the conversion ofcyclohexanone to monocyclohexylamine.

Recent technological developments in the production of cyclohexanonehave made this ketone potentially attractive as a raw material for theproduction of cyclo hexylamine. A raw material which is now potentiallyvery attractive is a mixture of cyclohexanol and cyclohexanone which hasrecently become available. However, there has not been a satisfactorymethod for the commercial reductive amination of cyclohexanone tocyclohexylamine. Of the five routes to cyclohexylamine which are listedin the text by Wagner and Zook, Synthetic Organic Chemistry, John Wileyand Sons, Inc, New York, page 684, the best yields reported are thoseobtained by the hydrogenation of an unsaturated aromatic amine,specifically aniline (94% yield), and the Worst yield reported was thatobtained by the reductive amination of cyclohexanone (using Raneynickel; 50% yield).

An object of this invention is provide a method for the production ofcyclohexylamine using cyclohexanone as a raw material. Another object ofthis invention is to provide a method for producing monocyclohexylaminein improved yields based on the cyclohexanone converted. A furtherobject of this invention is to provide a method which produces improvedyields of monocyclohexylamine from cyclohexanone when the ketone ispresent in a mixture of cyclohexanone and cyclohexanol. An object ofthis invention is to provide a method by which cyclohexanone isconverted directly to cyclohexylamine without requiring separateconversion to material more amenable to conversion to cyclohexylamine. Afurther object of this invention is to provide a method" for convertingcyclohexanone to cyclohexylamine by which substantially notricyclohexylamine is formed.

These and other objects which will be apparent hereinafter weaccomplished in accordance with this invention by a method comprisingcontacting cyclohexanone vapor with a stoichiometric excess of ammoniaand hydrogen in an ammonia-hydrogen gas mixture, said contacting takingplace in the presence of a specially prepared nickel catalyst at atemperature below about 230 C. and at a pressure between about 1atmosphere and about 8 atmospheres, said specially prepared nickelcatalyst having been reduced at a temperature below about 450 C.,reoxidized by passing a gas containing free oxygen over the reducedcatalyst and again reduced by passing a gas thereover containing freehydrogen at a temperature below about 250 C. The specially preparednickel 3,415,881 Patented Dec. 10, 1968 catalyst employed in the processof this invention is a nickel catalyst, e.g., nickel hydrate which hasbeen reduced at a temperature below about 450 C.,feoxidized by passing agas containing free oxygen 'over the reduced catalyst, preferably untilthe ratio of reduced nickel to total nickel is between about 55% andabout At this point a preferred catalyst contains about.5 8% totalnickel. The final reduction of the specially prepared nickel catalystcan then be accomplished in an eminently satisfactory manner by passinga gas thereover initially containing about 5% hydrogen and aboutnitrogen and thereafter progressively increasing the hydrogen content ofthe final reduction gas to so that the temperature of the latterreduction step is maintained below about 250 C. In an alternativepreferred procedure, the final reduction of the specially preparednickel catalyst is accomplished by contacting therewith pure hydrogengas, the initial contacting temperature being about C., maintaining thetemperature below about 250 C. The specially prepared nickel catalystmay be used as such, or it may be supported on any suitable support suchas kieselguhr, alumina, pumice, alundum, charcoal, or the variousnatural or synthetic clay-like supports that are well known to the art.In addition, the specially prepared catalyst composition may be modifiedif desired to incorporate certain basic substances or promoters, such assodium silicate, calcium oxide, magnesium oxide, zirconium oxide, or thelike.

The pressures employed in accordance with this invention during thecontacting of the cyclohexanone, ammonia, and hydrogen in the presenceof the special catalyst of this invention are atmospheric or nearatmospheric pressures. Pressures below about 8 atmospheres are eminentlysatisfactory, though pressures between about 2 and about 5 atmospheresare preferred.

The temperature for contacting the special catalyst with cyclohexanone,ammonia, and hydrogen in a preferred embodiment of this invention isbetween about 130 C. and about 180 C. Contacting temperaturessubstantially in excess of about 230 C. lead to the formation ofexcessive quantities of decomposition products such as cyclohexane.

We know of no true lower temperature limit however, and the practicallower operating temperature is governed primarily by economicallyacceptable rates of conversion. Below about 100 C. the rate ofconversion is comparatively slow. Hence, in accordance with thisinvention we prefer to employ temperatures above about 100 C; and belowabout 230 C., and it is more preferable to employ temperatures betweenabout 130 C. and about 180 C.

Hence, for each operating temperature there is a certain feed rate abovewhich conversion will begin to drop below about 100%. Therefore, if lessthan quantitative conversion is obtained under a specific set ofconditions either raising the temperature or lowering the feed rate willfacilitate achievement of complete conversion. At 100 C. about 0.1 poundof feed per pound of specially prepared nickel catalyst per hour cangenerally be completely converted in accordance with this: invention. Atabout 130 C. the upper feed rate for 100% conversion is about 0.3 poundsper pound per hour and it is about twice that rate at about 200 C. It isto be understood that these feed rates are not actually operative limitsand higher feed rates can be employed without departing from thisinvention. There is no nonoperative lower limit on the feed rate at anytemperature.

Generally speaking, higher recycle rates and higher levels of ammonia inthe ammonia-hydrogen gas mixture lead to lower conversion todicyclohexylamine. Ammonia-hydrogen gas mixtures containing ammonia inan amount between about mole percent and about 90 mole percent based onthe number of moles of said gas mixture are eminently satisfactory foruse in accordance with this invention. Ammonia-hydrogen gas mixturescontaining about 50 to about 90 mole percent ammonia on the same basisare preferred.

Hydrogen make-up gas and ammonia make-up gas are normally added to therecycling excess gas mixture leaving the product tank, and thereplenished gas mixture is passed through the vaporizer and on to thereactor catalyst bed. As used herein, the terms recycle ratio andrecycle rate refer to the ratio representing the number of moles ofammonia-hydrogen gas mixture per mole of feed which is present in thegas-feed mixture immediately before the reactants contact the catalystbed. When cyclohexanone is the feed, the recycle rate is calculated onthe basis of moles of cyclohexanone fed, Whereas when a mixture ofcyclohexanone-cyclohexanol is used as the feed, the recycle rate iscalculated on the basis of the total moles of feed. In accordance withthis invention recycle ratios between about 10 and 100 are eminentlysatisfactory, while those between about and about 90 are preferred.

It is preferred that the condenser and product tank be so adapted thatthe gas mixture leaving the product tank contain a minimum amount ofmaterials other than ammonia and hydrogen. While the stoichiometricexcess of the ammonia-hydrogen gas mixture is recycled over the 'bed inthe normal practice of this invention, the feed materials, e.g.,cyclo-hexanone, are normally completely converted in a single pass overthe catalyst bed.

A more preferred embodiment of this invention comprises contactingcyclohexanone, dicyclohexylamine, and a stoichiometric excess of ammoniaand hydrogen in the presence of the specially prepared nickel catalystdescribed above and at the temperatures and pressures described above.The amount of the dicyclohexylamine present with the cyclohexanone feedis preferably approximately the same as the amount of dicyclohexylaminein the degassed, dried, crude reaction product obtained from thereactor. Hence, if the crude reaction mixture is found to containapproximately 80% of monocyclohexylamine and 10% dicyclohexylamine byweight, based on the weight of the degassed, dried, crude product, thisamount (i.e., 10% by weight based on the weight of the feed) ofdicyclohexylamine is added to the cyclohexanone-containing feed inaccordance with the more preferred embodiments of this invention.However, it is not essential that the feed contain the same amount ofdicyclohexylamine as the product. Dicyclohexylamine in the feed inamounts between about 5% and about 25% by Weight based on the weight ofthe feed are generally useful, though larger or smaller amounts are alsouseful. In most cases an amount between about 5% and about 15% ispreferred.

The inclusion of the dicyclohexylamine in the feed material has beenfound to inhibit formation of more dicyclohexylamine from the feedmaterials. In a particular case in which the crude product is found tocontain 80% monocyclohexylamine and 10% dicyclohexylamine, the inclusionof approximately 10% dicyclohexylamine with the feed surprisingly altersthe direction of the conversion of the feed so that the yield ofmonocyclohexylamine is increased from about 80% based on thecyclohexanone converted to approximately 90% on the same basis, whileconversion of the feed to dicyclohexylamine is substantially suppressed.

We have found that this surprising suppression of the conversion ofcyclohexanone to dicyclohexylamine due to the presence ofdicyclohexylamine is achieved whether the specially prepared nickelcatalyst of this invention is employed or whether any of the lessefficient reductive amination catalysts of the prior art, such as Raneynickel, are employed, or whether the catalysts of Group VIII, such aspalladium or rhodium, are employed, as taught herein. Hence, we havealso discovered a method for obtaining improved yields ofmonocyclohexylamine comprising contacting cyclohexanone vapor with astoichiometric excess of ammonia and hydrogen in an ammoniahydrogen gasmixture, said contacting taking place in the presence of a hydrogenationcatalyst such as those of Group VIII, preferably palladium or rhodium,more preferably the special nickel catalyst described herein, saidcontacting also taking place in the presence of dicyclohexylamine in anamount substantially equal to the amount of dicyclohexylamine in thecrude product produced by said process, said contacting furthermoretaking place at a temperature below about 230 C., and at a pressurebetween about 1 atmosphere and about 8 atmospheres, preferably betweenabout 2 and about 5 atmospheres.

For example, in one pair of tests, 10 parts of feed per part of rhodiumper hour was fed in the vapor phase over a 0.5% 'rhodium on-aluminacatalyst. The feed was in an ammonia-hydrogen gas mixture containing 70mole percent ammonia. The contacting temperature was 100 C. and therecycle ratio, as defined above, was 40 to 1. In a run in which the feedwas cyclohexanone only, 100% conversion of the feed led to yield ofmonocyclohexylamine, and 8% dicyclohexylamine. In another test,identical except that the feed was cyclohexanone with 10%dicyclohexylamine, conversion of the cyclohexanone led to 88% yield ofmonocyclohexylamine with 0.1% yield of dicyclohexylamine.

In another pair of tests, 17 parts of feed per part of palladium was fedin the vapor phase over a 0.3% palladium-on-alumina catalyst. The feedwas in an ammonia'hydrogen gas mixture containing 65 mole percentammonia, the contacting temperature was C., and the recycle ratio, asdefined above, was 43 to 1. In a test in which the feed wascyclohexanone alone, 100% conversion led to 72% yield ofmonocyclohexylamine and 9% yield of dicyclohexylamine. In the duplicaterun, identical except that the feed contained 90% cyclohexanone, and 10%dicyclohexylamine, 100% conversion of the cyclohexanone led to 77%monocyclohexylamine and no dicyclohexylamine.

Use of dicyclohexylamine in conjunction with the special nickel catalystof this invention is illustrated further in the numbered examples. Thepreferred temperatures, pressures, recycle ratios, gas mixturecompositions, and other preferred operating variables will vary somewhatfor other catalysts of Group VIII from those taught above for use withthe special nickel catalyst of this invention, when these catalysts areused with dicyclohexylamine as taught herein.

The invention will be further illustrated but is not limited by thefollowing examples in which the quantities are stated in parts by weightunless otherwise indicated, in which the percent yields refer to molepercent of the converted feed which was converted to that particularproduct, and in which yields are based on product analyses which wereobtained by vapor phase chromatography of the benzene solution remainingafter removal of the water by azeotropic distillation of an aliquot ofthe crude product in benzene.

Example 1 A specially prepared nickel catalyst for use in the process ofthis invention was prepared and stabilized by the following procedure.Unreduced nickel oxide kieselguhr tablets were loaded into a verticaljacketed reactor tube. The system was purged with nitrogen and broughttoabout 260 C. by means of recirculating oil in the reactor jacket.Hydrogen flow was started and the temperature of the bed was graduallyincreased to about 427 C. The hydrogen-nitrogen mixture coming from thereactor tube passed through a condenser hermetically joined therewithand by way of a product drop-out tank and a recycle pump was returned tothe catalyst containing reactor tube. Water was removed from therecycling nitrogenhydrogen gas mixture by means of the condenser andproduct tank, and whenthe formation of water had virtually stopped, thesystem was cooled to about 32 C. while maintaining recycling hydrogenflow. When the catalyst bed had reached this temperature, the system waspurged with nitrogen. The reduced catalyst bed was then partiallyreoxidized by adding a small quantity of oxygen with the nitrogen.During the reoxidation step the temperature of the bed was maintainedbelow about 57 C. by adjusting the amount of oxygen present in therecycling oxygennitrogen mixture. The portion of the bed beingreoxidized was readily determined by observing the peak temperature bymeans of a sliding thermocouple inserted in a small tube located in thecenter of the bed and extending along the entire axis of the cylindricalcatalyst bed. When the 'peak temperature reached the bottom of thereactor, the stabilization was considered completed. Afterstabilization, the system was flushed with air to atmospheric conditionsand the specially prepared catalyst removed therefrom. In this form, thecatalyst contained about 60% nickel with the weight ratio of reducednickel to total nickel of about 55: 100.

Example 2 Nickel catalyst prepared and stabilized as in Example 1 (2200parts) was charged to a jacketed 1.3" inside diameter (I.D.) steelreactor tube included in a hermetically joined cyclic system comprisinga recycle compressor, flow meter, vaporizer, reactor tube, condenser,and product tank. The cyclic system was fitted with an analyticalinstrument especially adapted for determining the molecular weight ofthe recycled gas. The resulting cylindrical catalyst bed was heated bymeans of circulating oil in the jacket surrounding the reactor column.The gas in the entire system was purged with nitrogen gas. The catalystbed was heated to 140 C. by means of the circulating oil in the reactorjacket. The catalyst was reduced by passing pure hydrogen down throughthe column starting at about 140 C. Over a period of about 4 hours thetemperature of the recirculating oil was gradually raised to about 200C. and held there until no further water was recovered from therecycling gas stream by the cold water-cooled condenser. Thereupon,additional hydrogen and ammonia gas were forced into the recycling gasstream until the pressure of the gas at the catalyst bed wasapproximately 46 pounds per square inch gauge (p.s.i.g.). The ammoniagas and hydrogen gas were introduced into the system in such a way as toprovide a recycling gas having a molecular weight of about 12. Therecycled gas, therefore, was approximately 65 mole percent ammonia.Cyclohexanone was pumped into the vaporizer which was maintained at atemperature of 210 C. at the rate of 663 parts of cyclohexanone perhour. The recycling gas flow rate was adjusted to provide 44 moles ofgas per mole of cyclohexanone fed and the hydrogen and ammonia make-upwere adjusted to maintain approximately 46 pounds of pressure on thesystem and to maintain a molecular weight of about 12 in the recyclinggas. The oil circulating in the reactor jacket was maintained at about200 C. throughout this test. These conditions were maintained forapproximately 48 hours at which time a sample of the product was removedfor analysis. It was found that the cyclohexanone was 100% converted andthat monocyclohexylamine was produced in approximately 81% yield.Dicyclohexylamine was also produced in approximately yield along withcylohexane in 1.3% yield, aniline in 0.7% yield, cyclohexanol in about1% yield, and benzene in about 7.5% yield. No tricyclohexylamine wasfound in the product of this run.

Example 3 After the completion of the run described in Example 2, thefeed material was changed to a mixture of half cyclohexanol and halfcyclohexanone. This mixture was pumped into the vaporizer at the rate of723 parts of mixture per hour. The pressure of the gas in the reactorwas maintained at about 47 p.s.i.g. and the molecular weight of therecycling gas was maintained at about 13. The recycle rate was adjustedto provide approximately 41 moles of gas per mole of feed mixture. Therecirculating oil in the jacket of the reactor was maintained at 195 C.After 36 hours of operation, a sample of the product being condensedfrom the system was analyzed and it was found that the cyclohexanonemixture was undergoing 99% conversion to provide monocyclohexylamine inabout 81% yield and dicyclohexylamine in about 10% yield. Notricyclohexylamine was found in the product of this run. About 2% of thecyclohexanol fed was found in this product.

It is observed from Examples 2 and 3 that about 10- 11%dicyclohexylamine was being produced in the reaction in accordance withthis invention as described in those examples. The following exampleillustrates a more preferred embodiment of this invention in which thefeed contains dicyclohexylamine in an amount substantially equal to theamount appearing in the crude reaction product, and by which formationof additional dicyclohexylamine is substantially reduced.

Example 4 After the run of Example 3 was completed, thecyclohexanol-cyclohexanone feed was modified by admixing therewithsufficient dicyclohexylamine to provide a feed containing about 10% byweight dicyclohexylamine. This modified mixture was pumped to therecycle system vaporizer at the rate of about 680 parts per hour. Thegas was recycled at sufficient rate to provide 43 moles of recycled gasper mole of feed in the vaporizer. The hydrogen and ammonia make-uprates were adjusted to provide approximately 46 p.s.i.g. pressure on thesystem and recycled gas having a molecular weight of 13. The oilcirculating in the jacket surrounding the catalyst bed was maintained atabout 195 C. After 36 hours of operation, the product coming fro-m thereactor was sampled and it was found after correcting for thedicyclohexylamine in troduced with the feed that 99% of thecyclohexanolcyclohexanone mixture was converted to providemonocyclohexylamine in approximately 91% yield, dicyclohexylamine in2.8% yield, cyclohexane in about 1.1% yield, benzene in about 4.2%yield, and aniline in about 0.9% yield. No cyclohexanone ortricyclohexylamine was found in the product of this run.

Example 5 After the run of Example 4 was completed, the temperature ofthe oil circulating in the reactor jacket was lowered to 180 C. and allother operating conditions were maintained the same as in Example 4.After 36 hours of operation under these conditions, the product beingcondensed out of the system was analyzed and it was found that aftercorrecting for the dicyclohexylamine introduced with the feed mixturethat 99% of the cyclohexanol-cyclohexanone mixture had been converted toprovide monocyclohexylamine in about 91.5% yield, dicyclohexylamine inabout 2.8% yield, cyclohexane in about 0.1% yield, benzene in about 2.0%yield, and aniline in about 0 .2% yield. No tricyclohexylamine was foundin the product of this run.

Example 6 The test of Example 5 was repeated except that the recycleratio was lowered to 33:1, the temperature was 151 C., and the feedmaterial was cyclohexanone containing no dicyclohexylamine. Analysis ofthe product of this test indicated that substantially 100% conversionwas achieved to provide monocyclohexylamine in 93.8% yield anddicyclohexylamine in 6.6% yield.

Example 7 The test of Example 6 was repeated except that the feedmaterial was cyclohexanone containing about 8% by weightdicyclohexylamine based on the weight of the feed. Analysis of theproduct of this test indicated that substantially 100% conversion wasachieved to provide monocyclohexylamine in 97.5% yield anddicyclohexylamine in 1.9% yield.

Example 8 Nickel catalyst prepared and stabilized as in Example 1 (655parts) was charged to a /4" LB. jacketed steel reactor tube in a systemsuch as that described in Example 2. The catalyst bed was reduced by aprocedure such as that described in Example 2, and after the catalystwas reduced, ammonia gas and hydrogen were introduced to the system insuch a manner as to provide 46 p.s.i.g. pressure and a recycled gasmolecular weight of 13. A feed mixture containing approximately 90%cyclohexanone and 10% dicyclohexylamine was pumped at the rate of 150parts per hour into the vaporizer which was maintained at 200 C. The oilbeing circulated in the jacket around the reactor was maintained at 195C. After 16 hours of operation under these conditions, the product beingcon-- densed from the system was sampled, and it was found that aftercorrecting for the dicyclohexylamine added with the feed 100% of thecyclohexanone was converted to provide cyclohexylamine in about 90.5%yield, dicyclohexylamine in about 0.6% yield, cy'clohexane in about 0.8%yield, .and aniline in about 1.8% yield. No cyclohexanol ortricyclohexylamine was found in the product of this run.

In the above examples numbered 2 through 8 considerable gas evolution oreffervescence was encountered upon emptying the pressurized producttank. It is believed that some of the product compounds may have beenlost as sweep-out during this degassing step and it is further believedthat this is the main reason Why the theoretical yields of the aboveexamples did not add up to 100%.

It is clear from the above examples, however, that we have provided amethod for producing monocyclohexylamine in improved yields fromcyclohexanone. The special nickel catalyst of this invention is found toprovide long life when used in accordance with this invention. In bedsused for a series of tests in accordance with this invention, such asthose of the examples above, no sign of lessening of catalytic activityor build-up of material on the catalyst bed appeared, even though someseries were continued until over 100 pounds of feed were contacted perpound of catalyst.

Therefore, we claim:

1. In a method for producing monocyclohexylamine by the reductiveamination of cyclohexanone, said method providing a crude productcontaining dicyclohexylamine, the improvement comprising contactingcyclohexanone with a stoichiometric excess of ammonia and hydrogen in anammonia hydrogen gas mixture, said contacting taking place in thepresence of a hydrogenation catalyst and also in the presence ofdicyclohexylamine, said dicyclohexylamine being present in an amountsubstantially equal to the amount of dicyclohexylamine contained incrude product, said amount being between about 5% and about 25% byweight of the feed, said contacting taking place at a temperature belowabout 230 C. and at a pressure between atmospheric pressure and aboutfive atmospheres.

2. A method as in claim 1 in which said pressure is between about twoand about five atmospheres.

3. A method as in claim 1 in which the hydrogenation catalyst is anickel catalyst having been prepared from nickel oxide reduced at atemperature below about 450 C., reoxidized by passing a gas containingfree oxygen over the reduced catalyst and again reduced by passing a gasthereover containing free hydrogen at a temperature below about 250 C.

4. In a method for producing monocyclohexylamine by the reductiveamination of cyclohexanone, said method providing a crude productcontaining dicyclohexylamine, the improvement comprising contacting acyclohexanonecontaining feed mixture with a stoichiometric excess ofammonia and hydrogen in an ammonia-hydrogen gas atmosphere, saidcontacting taking place in the presence of a hydrogenation catalyst,said feed mixture also containing dicyclohexylamine in an amountsubstantially equal to the dicyclohexylamine present in the crudeproduct, the amount of dicyclohexylamine present in the feed mixturebeing between about 5% and about 25% by weight based on the weight ofthe feed, said contacting taking place at the temperature below about230 C. and at a pressure between about two atmospheres and about fiveatmospheres.

5. A method as in claim 4 in which the hydrogenation catalyst is anickel catalyst having been prepared from References Cited UNITED STATESPATENTS 6/1930 Reppe. 12/1934 Ernst et al.

OTHER REFERENCES Alexander et 211., J.A.C.S., vol. 70, 1315 (1948),

CHARLES B. PARKER, Primary Examiner.

P. C. IVES, Assistant Examiner.

US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,415,881 December 10, 1968 Andrew P. Dunlop et al.

It is certified that error appears in the above identified patent andthat said Letters Patent are herebycorrected as shown below:

Column 7, line 9, (655 parts)" should read (665 parts) Signed and sealedthis 31st day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. JR.

Attesting Officer Commissioner of Patents

